The suspicion was always that, so long as they weren't overrun in the middle, Tottenham would prosper in wide areas against a very narrow AC Milan side, and that was precisely what happened. What was not expected, though, was quite how comprehensively Spurs would dominate the middle, or that they would pose such an attacking threat even without the injured Gareth Bale, who had twice tormented Milan's neighbors Internazionale in the group stage.
Harry Redknapp makes a virtue of being bluff and English and having little time for fancy foreign ideas like tactics, but he is far more astute than the common perception allows. He had vowed to attack Milan, pretending his side could do no different -- and Spurs had been the only side in Champions League history to score at least twice in each of their six group games -- and in the early stages that's exactly what Tottenham did, constantly working the ball wide to the right for Aaron Lennon and sending crosses to the back post where Peter Crouch kept pulling deep, into the awkward area between Alessandro Nesta and Ignazio Abate.
The key, though, was the way Spurs were able to dominate the middle and so win enough possession to work it wide, and it may be, heretical as it may sound, that they were aided in that by the absence of Bale.
The selection of Steven Pienaar ahead of Niko Kranjcar, who had played on the left in the preceding two league games, meant Spurs were a little narrower than usual through the middle -- they had done something similar in the 2-1 win against Arsenal last season -- and so were able to compete more evenly with Milan's 4-3-1-2 in central areas.
Milan's problem -- indeed the problem with the 4-3-1-2 generally -- is that while it offers defensive resilience, it can become predictable if the fullbacks, who are supposed to provide width, are penned in; everything has to go through the trequartista -- Clarence Seedorf in this instance -- and he as stifled by Spurs' two holding midfielders, Wilson Palacios and Sandro. Neither have been regulars this season; both were superb in the San Siro, holding their positions in front of the back four with supreme discipline.
The introduction of Pato for Seedorf gave Milan more dynamism in the second half, although they still seemed sluggish beside Tottenham, something that, alongside Roma's supine display against Shakhtar Donetsk on Wednesday, exposes the general sedateness of Serie A. Even then, the only real chances Milan created were the two headers from Mario Yepes, and given Tottenham's clear pace advantage, a breakaway was always likely. When it came, it was with glorious inevitability, Aaron Lennon given 40 yards to run at Yepes, a near impossible position for a defender.
In that the contrast between Milan and Spurs was clear. It would be easy to suggest this was a victory for the Premier League side's great pace and physicality -- and to an extent it was -- but it was also a tactical triumph, for where Milan, having blanketed its center backs with three midfield holders left them exposed for one crucial, fatal moment, Palacios and Sandro never faltered.
There are two diametrically opposed theories as to the best way to deal with Barcelona. An opponent can sit men behind the ball, occupy the center, and hope to deny Pep Guardiola's side the space to pass its way through to goal. That's what Internazionale did in eliminating Barca in the semifinal last season, and what Sporting Gijon did in forcing a draw last weekend. Or an opponent can try to press Barca high up the pitch, to play it at its own game, effectively. That's what Espanyol did earlier in the season; it rattled Barca, perhaps caused it more problems than any other team this season, and yet it lost 5-1, as Barca picked it off on the break as legs tired late on.
Sitting deep is so alien to Arsenal's usual way of doing things that it was always likely Arsene Wenger would opt for the latter. When the sides met in the quarterfinal last season, the gulf between the sides lay less in anything technical than in the superiority of Barca's pressing. Not only was it hard to take the ball from Barca, Arsenal also struggled to keep hold of it for any length of time. The result was an opening 20 minutes at the Emirates in which Arsenal could have been humiliated but for an improbable string of excellent saves from Manuel Almunia.
Barca produced nothing similar on Wednesday -- in fact, it was Arsenal who started the better. It still could easily have been more than 1-0 up at half-time -- Lionel Messi missed one chance he would usually score and had a goal ruled out for an extremely tight offside -- but it never achieved the same levels of dominance, partly because of the excellence of Jack Wilshere, who gave a majestically composed display at the back of Arsenal's midfield. Barca was still on top -- when both sides favor a possession game, to win that battle 60%-40% suggests a significant advantage -- but never to the same degree.
A basic truth of the sort of hard pressing Barca favor is that it is impossible to maintain for 90 minutes. Barry Hulshoff said the Ajax of the seventies could press for around 70 minutes. Under Valeriy Lobanovskyi, Dynamo Kyiv used to "false press" during games to give itself a rest from true pressing. Barca rarely presses from start to finish, and if it does hard press from the start, it often has such a commanding lead, or has so shattered the opposition, that a drop-off in intensity in the final quarter of the game barely matters. Both last season and this, Arsenal enjoyed its best spell in the final 20 minutes at the Emirates.
Some have suggested that replacing David Villa with Seydou Keita after 68 minutes was a tactical error from Guardiola, handing the initiative to Arsenal; in fact, adding a holding player was a natural response to the knowledge that it would be impossible to maintain the hard press.
Whether by coincidence or design, it was at the same time that Arsenal brought Andrey Arshavin on for Alex Song and so adopted a more attacking approach. With that in mind, it may be that the pace of Theo Walcott, which will always terrify a side that plays a high line, may be best deployed off the bench against tiring legs.
Those changes were enough to shift the momentum fractionally in Arsenal's favor and with a goalkeeping error and a brilliant counterattack, that was enough to earn them a win. It was a superb performance -- just to live with Barcelona requires astonishing energy, application and organization -- and a magnificent win, but there needs to be a level of realism. Excellent as it was, Arsenal rode its luck, and it will take an even more extraordinary display in the Camp Nou to win the tie.
Jonathan Wilson is the author of Inverting the Pyramid; Behind the Curtain; Sunderland: A Club Transformed; and The Anatomy of England.